1. Field of the Invention
The present invention is broadly concerned with fill compositions and methods useful for protecting the surfaces forming the contact and via holes during dual damascene processes for the production of integrated circuits. More particularly, the compositions of the invention comprise a quantity of solid cross-linkable components including a polymer binder, and a solvent system for the solid components. The boiling point of the solvent system is preferably sufficiently lower than the cross-linking temperature of the composition so that essentially all of the solvent system is evaporated during the first stage bake without the fill composition being cross-linked to any appreciable degree. In use, the fill compositions are applied to a substrate previously patterned with contact or via hole according to conventional methods followed by heating the composition to its reflow temperature in order to evaporate the solvent system and cause the composition to flow into the hole for uniform coverage. The composition is then cured and the remainder of the dual damascene process carried out in the usual fashion.
2. Description of the Prior Art
The damascene process, or the process of forming inlaid metal patterning in preformed grooves, is generally a preferred method of fabricating interconnections for integrated circuits. In its simplest form, the dual damascene process starts with an insulating layer which is first formed on a substrate and then planarized. Horizontal trenches and vertical holes (i.e., the contact and via holes) are then etched into the insulating layer corresponding to the required metal line pattern and hole locations, respectively, that will descend down through the insulating layer to the device regions (if through the first insulating layer, i.e., a contact hole) or to the next metal layer down (if through an upper insulating layer in the substrate structure, i.e., a via hole). Metal is next deposited over the substrate thereby filling the trenches and the holes, and thus forming the metal lines and the interconnect holes simultaneously. As a final step, the resulting surface is planarized using the known chemical-mechanical polish (CMP) technique, and readied to accept another dual damascene structure.
During the dual damascene process, the contact and via holes are typically etched to completion prior to the trench etching. Thus, the step of trench etching exposes the bottom and sidewalls (which are formed of the insulating or dielectric layer) of the contact or via holes to over-etch which can deteriorate the contact with the base layer. An organic material is therefore used to partially or completely fill the via or contact holes and to protect the bottom and sidewalls from further etch attack. These organic fill materials can also serve as a bottom anti-reflective coating (BARC) to reduce or eliminate pattern degradation and line width variation in the patterning of the trench layer, provided the fill material covers the surface of the dielectric layer.
Fill materials have been used for the past several years which have high optical density at the typical exposure wavelengths. However, these prior art materials have limited fill properties. For example, when the prior art compositions are applied to the via or contact holes formed within the substrate and to the substrate surface, the films formed by the compositions tend to be quite thin on the substrate surface immediately adjacent the holes, thus leading to undesirable light reflection during subsequent exposure steps. Also, because the prior art compositions etch more slowly than the dielectric layer, the unetched fill compositions provide a wall on which the etch polymer will deposit. This etch polymer build-up then creates undesirable resistance within the metal interconnects of the final circuit. These problems are explained in more detail below.
There is a need in the art for contact or via hole fill materials which provide complete coverage at the top of via and contact holes. Furthermore, this material should provide adequate protection to the base of the via and contact holes during etching to prevent degradation of the barrier layer and damage to the underlying metal conductors. In order to prevent sidewall polymer buildup, the etch rate of the material should be equal to or greater than the etch rate of the dielectric material, or the contact or via holes should be filled partially so that the fill material in the holes does not extend above the base of the trench following trench etch.